Comparison Study on Damage Characteristics of Deeply Buried Granite Under Triaxial Cyclic Loading and Unloading

The scope and degree of damage are crucial for the stability of deep underground engineering during construction and operation. This study investigates the damage evolution characteristics of deeply buried granite throughout the entire process of triaxial cyclic loading and unloading compression experiments under different confining pressures. The research first focuses on the evolution patterns of deformation parameters, energy dissipation, and acoustic emission (AE) activity. Subsequently, a comparative analysis of six different damage quantification methods was conducted to identify the most suitable method. The results show that, with increasing axial strain, the elastic modulus first increases and then decreases, while the Poisson's ratio gradually increases. The increase in confining pressure leads to an overall increase in both elastic modulus and Poisson's ratio. As the axial strain increases, the dissipation ratio initially decreases, then increases, and finally stabilizes, while the crushing ratio first increases, then decreases, and ultimately stabilizes. AE activity shows a clear Kaiser effect and silence phenomenon, with a strong correlation between the post-peak strength degradation and AE counts and AE energy. The evolution patterns of damage variables for the six quantification methods all exhibit S-shaped growth, with damage rates showing a slow-fast-slow variation. The damage variable defined by the crushing energy method aligns with the crack propagation law and has the smallest error in damage threshold compared to existing standards. The results of this study provide important references for rock damage testing and quantification. A novel method for identifying the deflection point of the stress-strain curve.Multi-perspective observation of damage evolution in deep rock.Theory of nonlinear dissipation of crushing energy considering confining pressure effects.Optimal damage characterization method based on standards and crack propagation laws.